1. Field of the Invention
The present invention relates to a unit battery of sealed alkaline storage battery of relatively large cape city and to a sealed alkaline storage battery system.
2. Description of Prior Art
Sealed alkaline storage batteries are represented by nickel.cndot.cadmium storage batteries and nickel.cndot.hydrogen storage batteries and are high in energy density and excellent in reliability. Therefore, they are widely used as electric sources for portable apparatuses such as videotape recorders, lap-top type computers and pocket telephones.
These are mainly small-sized sealed alkaline storage batteries which comprise a metallic container, have a cylindrical or rectangular shape and have a capacity of about 0.5-3 Ah. In actual use, several to several ten cells are put in a resin container or tube.
Since these small-sized sealed alkaline storage batteries have a capacity of about 0.5-3 Ah, the quantity of heat generated at the time of charging and discharging per cell is small. Accordingly, when they are used in a resin container or tube, generation of heat and dissipation of heat are properly balanced and so there has been no serious problem resulting from the rise of temperature of batteries. Furthermore, electrode group of alkaline storage batteries expand due to repetition of charging and discharging, but the container is in the form of a metallic cylinder and there have been no problems such as distortion of the container due to expansion of the electrode group. For the rectangular container, since the battery is small, no special means has been needed.
However, recently, medium-sized and large-sized batteries of high energy and high reliability (here, the medium-sized battery is defined to be one having a capacity of 10-100 Ah and the large-sized battery is defined to be one having a capacity of higher than 100 Ah and several to several hundred cells are used) are strongly demanded as portable electric sources for house hold appliances and electric cars. As the medium-sized and large-sized batteries, open nickel.cndot.cadmium batteries or lead storage batteries are used for storage of energy and for UPS, but there are troubles in maintenance such as filling of electrolyte during period of service. Therefore, maintenance free batteries, namely, sealed batteries are necessary as portable electric sources for household appliances, electric cars and the like. As explained above, when alkaline storage batteries are used as portable electric sources for household appliances, electric cars and the like, sealed and medium-sized or large-sized batteries are necessary.
That is, it is necessary to connect many cells in series for increasing electric capacity of cells and cell voltage with sealed cells.
A cell generates heat of reaction due to the electrode reaction and Joule's heat by charging and discharging. Quantity of heat generated increases due to increase in electric capacity of cells and by sealing of the cells, and dissipation of heat to outside is delayed. Thus, the generated heat is accumulated in the battery and as a result, the temperature in the battery is higher than that in the small-sized batteries. Furthermore, in the container of a unit battery consisting of the cells of such large capacity connected in series or an assembled battery consisting of unit batteries connected in series, several ten cells to several hundred cells are arranged adjacent to each other. In order to solve the above problems, Japanese Patent Kokai (Laid-Open) No. 3-291867 proposes a heat dissipation device for a storage battery system in which a large number of cells which are composed of positive electrodes, negative electrodes and an electrolyte and which generate heat at the time of charging are arranged, characterized in that spaces are provided between the cells, and width of space/width of cell is in the range of 0.1-1.0.
However, in spite of these attempts, the above storage battery system still has the following problems in actual use.
1 Since the electricity generating element expands due to repetition of charging and discharging, the container is distorted and the ratio, space width/cell width changes to render circulation of air difficult. In order to keep constant the space between the cells, it is necessary to improve the strength of the container. For improving the strength of the container, the thickness must be increased, and as a result, weight or volume of battery increases to cause substantial reduction of energy density of the battery.
2 The container expands owing to increase of internal pressure of the cell and it becomes difficult to keep constant the width of spaces between which the air circulated. In order to inhibit the distortion of the container due to increase of pressure in the cell, it is necessary to increase the strength of the container.
As in the container of 1, weight or volume of the container increases for increase of the strength of the container. As a result, weight energy density and volume energy density decrease.
For solving the problems of 1 and 2, it is necessary to inhibit distortion of the container at unit battery level (comprising about 5-40 cells).
3 Furthermore, if the container expands and is distorted, a space is produced between the electricity generating element and the container. If there is a space between the electricity generating element and the container, the velocity of transfer of the heat generated from the electricity generating element extremely reduces. Accordingly, it is necessary to strengthen the unit battery and to allow the container to contact always with the electrode group.
4 A system comprising many cells has been proposed, but when the system is used as a portable electric source, it is necessary to attain reduction of scattering in cell performances such as cell capacity of each of several to several hundred cells, improvement of cell performances such as energy density and furthermore, improvement of mechanical strength such as prevention of shifting of the cells in their position caused by shock in the form of a unit battery (comprising about 5-40 cells) or an assembled battery (comprising at least two unit batteries, namely, about 10-300 cells).